The invention relates to a safety device on a rope, comprising:                a first flange-plate and a movable second flange-plate delineating a transverse space in which a roller is arranged fitted on a first spindle integral to the first flange-plate,        and articulation means of the second flange-plate comprising a second spindle allowing a swivelling movement between a closed position clamping the rope in captive manner in the transverse space, and an open position for fitting the rope on the roller.        